Changes in the frequency and intensity of concurrent extreme wind speed and precipitation days over China during 1981–2022

Abstract. Compound extreme wind speed and extreme precipitation days (CWPDs) can significantly impact production and living, socio-economies, and human health. However, most previous studies have used fixed percentile thresholds to determine wind speed and precipitation extremes. This study investigated the characteristics and dynamics of CWPDs during 1981–2022 in mainland China based on the time-varying daily thresholds by using daily maximum wind speed and precipitation observation data. The results indicated that CWPDs were most likely to occur in southeastern South China (SC), Hainan Province, the northwestern parts of the middle and lower reaches of Yangtze River (YR), some scattered areas in the central and eastern YR. Annual CWPDs decreased in mainland China during 1981–2010, and then showed an obvious upward trend after 2010. Different percentile thresholds had effects on the spatial pattern and change trend of CWPDs. Spatially, CWPDs decreased more in parts of eastern Southwest China (SWC), YR, southeastern North China (NC) and central Northeast China (NEC), but less in mid-northern NC and most of Northwest China (NWC). In most areas of mainland China, the CWPDs frequencies under the four thresholds all showed decreasing trends, as the threshold increased, the trends of decreased for CWPDs frequencies decreased. With the increase of the threshold, the range of CWPDs with stronger intensity further reduced. CWPDs intensities were more severe in eastern coastal areas of YR, mid-eastern SC, parts of eastern SWC, parts of central NEC, parts of northwestern NWC and mid-northern in Hainan Province. Annual CWPDs intensities changed obvious around early-to-mid 2010s in under four different thresholds. With the increase of the threshold, the weakening trends of annual CWPDs intensities further weakened and even slightly strengthened during 1981–2022. The CWPDs intensities under the four thresholds all showed decreasing trends in most areas of mainland China except for parts of central SC, a few scattered areas of YR, several scattered areas of NC and NEC, a few scattered areas of NWC, individual areas of eastern SWC. As the thresholds increased, the trends of weakened for CWPDs intensities decreased and the scopes with a slight strengthening trend expanded. The changes of extreme wind speed days were consistent with those of CWPDs during 1981–2010 and 2011–2022, but the changes of extreme precipitation days and CWPDs were not corresponding. Due to the increase of extreme wind speed days and the accelerated increase of extreme precipitation days after 2010, the CWPDs changed from decrease before 2010 to increase after then. We conclude that the annual cumulative value obtained through time-varying thresholds and the latest daily observations can yield new insights into compound extremes.